The present invention refers to a device for determining the temperature in the interior of a vehicle.
Vehicles equipped with air-conditioner devices have a temperature sensor for sensing the temperature in the interior of the vehicle, which sensor is hidden, for design considerations, and mostly arranged in the control of the air conditioner. For the interior temperature sensor to measure the temperature of the air in the car interior, air flows passed the interior temperature sensor that is generated by a ventilating motor also provided in the control. To this end, the interior temperature sensor is located within a channel into which the ventilating motor draws air through an opening directed towards the car interior.
This concept of determining the interior temperature by measuring techniques has basically proven useful in practice. It should be noted, however that the known systems are not error-free. For example, the system is susceptible to failure due to the presence of the ventilation motor, both with regard to the electrics and to the continuity of the airflow. If, for example, the flow resistance increases due to a clogged air-inlet opening of the channel, the interior temperature sensor is no longer sufficiently ventilated and can therefore no longer provide measuring signals representing the interior temperature with sufficient accuracy. Moreover, the interior temperature sensor can become soiled by particles entrained in the flowing air and cause inaccuracies in the measurement. This risk is particularly high in cars carrying smokers. Several attempts have been made to realize temperature measuring in the interior of a vehicle by means of a xe2x80x9cnon-ventilatedxe2x80x9d temperature sensor.
German Patent 37 22 000, for example, describes a device for measuring temperatures in the interior of a space, using two temperature sensors. While one temperature sensor is located near an inner wall defining the interior and is surrounded by the air inside the space, a second temperature sensor is situated directly on the surface of the wall. Through a differential measurement of the output signals of both temperature sensors and with consideration to a decoupling factor, the actual interior temperature is determined. Another device for measuring the interior temperature is described in German Patent 41 30 063.
From German Patent 34 40 880, a temperature measuring device for determining the air temperature in the interior of a car is known, wherein a thermal conductor element is located close to a temperature-sensitive measuring element, the thermal conductor element itself being thermally coupled with an outer wall of the car interior. In this manner, the measuring signal of the measuring element also includes the influence of the temperature of the outer wall of the car interior, adjacent to the temperature measuring device, on the air temperature.
German Patent 198 16 941 discloses a temperature measuring arrangement wherein a thermal conductor element is arranged between a measuring point and a temperature sensor.
Finally, German Utility Model 88 12412 describes a temperature measuring sensor for a cooling tower, which, in order to suppress temporary variations of the air temperature to be measured, is located with good thermally conductive connection on a support plate that also has good thermal conductivity and is subjected to the medium to be measured.
Unfortunately, the known interior temperature measuring systems with non-ventilated sensors are not developed far enough to allow for an exact determination of the interior temperature in any temperature condition the car interior and the adjacent car elements may be in.
It is the object of the present invention to provide a device for determining the interior temperature of a vehicle, with which a precise measurement or determination of the temperature can be obtained.
According to the invention, the object is solved with a device for determining the temperature in the interior of a vehicle, comprising:
a temperature sensor for arrangement behind a wall adjacent to the interior,
a processing unit receiving the measuring signal from the temperature sensor and outputting an output signal representing the temperature in the vehicle interior, and
a thermal conductor element for sensing the temperature of the air of the interior within the region close to the wall, the thermal conductor element being in thermally conductive contact with the temperature sensor and is provided to extend up to or close to the wall or through an opening in the walls.
When mounting the present device in a vehicle, the temperature sensor intended to sense the temperature in the vehicle interior, is located behind a wall defining the interior. Preferably, this wall is the front bezel of the vehicle""s air conditioner control. However, any other wall or surface portion of the instrument panel with integrated or added components may be used. A thermal conductor extends through an opening in the wall, the thermal conductor being thermally coupled with the temperature sensor. By the thermal conductor, the thermal conductivity from the interior to the temperature sensor is improved. As an alternative, the thermal conductor extends to or close to the (rear side of the) wall. The thermal conductor may also be an integral part of the temperature sensor (a contact end if a Surface Mount Device (SMD) temperature sensor, for example).
The solution proposed by the invention allows to reliably and exactly measure the temperature in the interior of a vehicle. According to the invention, no ventilation system is required, whereby the function of the present device is improved and its service life is extended. Finally, the present approach is also less expensive. Under aspects of comfort, the present approach is further advantageous in that acoustic nuisances such as they are experienced with the operation of a ventilation motor, for example, are eliminated.
The thermal coupling between the temperature sensor and the thermal conductor element is suitably established by a contacting of the thermal conductor element and the housing of the temperature sensor, or by a thermally conductive connection of the thermal conductor element and one of the terminal contacts of the temperature sensor. The tatter possibility is of particular interest when the temperature sensor is a SMD component. Such a component has a relative large surface provided at its terminal contact ends and contacting the conductor paths of a circuit board. Thus, the conductor path may be used to thermally couple the temperature sensor and the thermal conductor element by also contacting the latter with the conductor path. The thermally conductive connection between the thermal conductor element and the temperature sensor is the better, the closer the contact points of the respective terminal contact end of the temperature sensor and the conductor path and of the thermal conductor element and the conductor path are arranged on the same.
Suitably, the thermal conductor element comprises a metal material or, more generally, a material with good thermal conductivity. For optical reasons, it may be advantageous to provide the thermal conductor element with a coating or to otherwise design it such that its surface possibly visible from the interior of the vehicle is similar or at least adapted to the wall behind which it is arranged or through which it extends.
In order to minimize the thermal influences of components, vehicle parts and the like provided in the vicinity of the temperature sensor, it is advantageous to enclose the temperature sensor, possibly together with the circuit board on which it is provided, with a thermal shield element formed from a thermally insulating material. The material used may be foamed plastics, for example, with open-cell foamed plastics being the material of choice.
In order to further minimize temperature influences from the environment of the temperature sensor, it is suitable to compensate for the temperature influence caused by irradiation of sunlight on a neighboring component or part. According to an advantageous development of the invention, this is realized by a first solar sensor that may be arranged in an opening in the wall and which is electrically connected with the processing unit. Thus, the processing unit receives the output signal from the solar sensor and uses the same to correct the sun-related influence of the heating of the wall around the wall opening in the measuring signal provided by the temperature sensor.
In particular, the first solar sensor is a solar sensor with which both the intensity and the angle of incidence of the solar radiation can be determined. This increases the exactness of the correction of the measuring signal from the temperature sensor.
Alternatively or in addition to a previously described solar sensor, the angle of incidence and the intensity can also be determined by another solar sensor generally located in the instrument panel of the vehicle and used mainly to control the vehicle""s air conditioner. From the output signal of this solar sensor, together with the output signal from the first solar sensor, the intensity and the angle of incidence of the sunlight in the region around the wall opening can be determined.
Depending on the position of the temperature sensor on the surface to be measured, the surface can be subject to more sunlight in the area of the temperature sensor when the sunlight impinges obliquely thereon than the solar sensor can detect. This is particularly true when, due to local conditions, the surface to be measured protrudes in the area of the temperature sensor and the solar sensor is provided in the part of the surface receding with respect to the projection. In this case, oblique irradiation by sunlight will impinge on the lateral faces of the projection under a different angle than determinable by the solar sensor. In this respect, one may employ the solar sensor arrangement usually present on the instrument panel when air conditioning is installed, which arrangement also measures the intensity of the sunlight. Assuming that all solar sensors are subject to the same solar radiation, a difference between the measuring signals from the solar sensor at the surface and the solar sensor on the instrument panel represents the angle of incidence of the solar radiation on the surface. From this, it may be concluded how much the projection of the surface, whose geometry and position relative to the solar sensor are known, is heated by solar radiation.
To compensate for thermal influences resulting from adjacent vehicle parts, it is advantageous to provide another temperature sensor that measures these thermal influences. In addition or as an alternative, these thermal influences can also be determined from calculation models or operation parameters of the adjacent vehicle components or parts. From these operation parameters, one may calculate an inherent heating. The sources of such inherent heating are, in particular, light sources in the vehicle component for back-lighting the front bezel, a display or the like. Taking the operation voltage of these possibly dimmable back-lights, one may draw conclusions as to the inherent heating to be expected.
Generally, a solar sensor, as described before, can be dispensed with, if the arrangement of the thermal conductor element projecting into the interior of the vehicle can be made such that the thermal conductor element is at least not subjected to direct solar radiation. It could be mounted, for example, in the foot area of the interior. However, it is preferred to position the device for determining the temperature in the interior of the vehicle in the upper and front part of the instrument panel. Here, a solar sensor should also be provided for correcting thermal influences on th temperature sensor due to solar radiation, as described before.
Such a solar sensor will project at least slightly beyond the front bezel of the control of the vehicle""s air conditioner, for example. The thermal conductor may now advantageously be arranged at the housing of the solar sensor. Thus, the thermal conductor may be provided in a region of the photo-sensitive outer surface of the solar sensor that cannot optically be detected by the passengers. This may be, for example, the part of the outer surface of the solar sensor that faces toward the vehicle floor. The thermal conductor could be arranged even less conspicuously when embedded or integrated into the outer surface of the solar sensor.
The solar sensor itself has electric terminal elements suitably connected to the conductor paths of a circuit board on which the temperature sensor is also provided. Advantageously, the thermal conductor element, one of the two terminal elements of the temperature sensor and one of the two contact elements of the solar sensor are contacted (e.g., by soldering), closely together, to a common conductor path. Thus, besides the actual thermal conductor element, one may also employ the electrode of the solar sensor connected to the relative terminal element of the solar sensor for assisting thermal conduction from the vehicle interior to the temperature sensor. This electrode extends through the (plastics) mass forming the housing of the solar sensor and is, thus, in a way, thermally decoupled from the interior. However, the distance from the electrode to the outer surface of the solar sensor is small so that the thermal decoupling has no excessive effect. In any case, employing the electrode of the solar sensor improves heat transfer from the interior of the vehicle to the temperature sensor, resulting in an increased precision of the temperature measurement.
In an advantageous development of the invention, it is provided that the processing unit comprises a differentiating member with a time constant for long-time differentiation of the measuring signal of the temperature sensor. The constant or, advantageously, variable time constant of the differential member preferably ranges from several minutes to several 10 minutes (e.g. 10 to 30 minutes) and, in particular, between 2 minutes and 15 minutes. According to the invention, the measuring signal of the temperature sensor and the differentiated measuring signal, i.e. the output signal of the differentiating member, are added in the processing unit. The sum of the two signals represents the temperature within the car interior. Thereby, the thermal inertia of components or the like surrounding the temperature sensor can be compensated. Instead of differentiating the output signal of the temperature sensor, the difference between the set and the actual values of the interior temperature can be subjected to differentiation. Therefore, the term xe2x80x9cprocessing unitxe2x80x9d as used in this specification is also meant to include the interior temperature control of a vehicle air conditioner. Thus, xe2x80x9cmeasuring signal of the temperature sensorxe2x80x9d also includes the deviation in the control circuit.
In an advantageous embodiment of the invention, the processing unit includes, in addition to the differentiating member, an amplification member with an amplification factor. This amplification member amplifies the differentiated measuring signal, i.e. the output signal of the differentiating member. Suitably, the time constant of the differentiating member and/or the amoplification factor of the amplification member are kept constant or varied. The variation is effected, in particular, in dependence on the possibly compensated measuring signal from the temperature sensor itself, the time laidup and/or the environmental temperature of the vehicle, the difference between the actual and the set values of the temperature in the car interior or between the actual and the set values of the temperature of the air flowing into the vehicle interior and/or the temperature of the coolant water.
Thus, the present invention suggests to sense the temperature in the interior of a vehicle by means of a temperature sensor arranged behind a surface or a wall defining the interior of the vehicle. The thermal conductor element increases the amount of heat transferred between the interior and the temperature sensor. Further, (parasitic) heat transfer is effected by inherent heating or a heating due to solar radiation on the surface or the wall behind which the temperature sensor is arranged or due to adjacent parts or vehicle components. Thus, the temperature sensor should be arranged in a suitable holder with small contact surfaces such that it receives and gives off only a minimum of heat from or to the adjacent vehicle parts, components or the like by thermal conduction. To minimize influences acting through thermal conduction through the air, it is feasible to provide a thermal shield element around the temperature sensor. To minimize thermal transfer via components (circuit boards, etc.) in contact with the temperature sensor, it is useful to make these parts from corresponding materials of relatively poor thermal conductivity. For example, the contact paths (conductor paths) leading to the temperature sensor could be made narrow and thin so as to realize a thermal decoupling between the temperature sensor and the electronics connected as well as the vicinity of the temperature sensor.
The thermal conductor element may also be provided behind a projection, e.g. at the rear thereof, of the wall delimiting the interior. By the fact that the thermal conductor element projects toward the interior with respect to the adjacent portion of the wall, the thermal conductor element extends xe2x80x9cthroughxe2x80x9d the wall, meaning that it protrudes relative to the adjacent wall portion. Further, the projection of the wall provides for a good thermal coupling between the thermal conductor element and the interior, because the surface of the projection is exposed to the interior. Moreover, there is a sufficient thermal decoupling from the wall.
In any case, the thermal conductor extends up to or close to the rear side of the wall. Possibly, the temperature sensor is provided directly at the rear side of the wall, its electric contact ends or terminals actingxe2x80x94depending on the respective designxe2x80x94as thermal conductors to improve heat transfer from the interior (front of the wall) to the temperature sensor.
Another alternative provides that the thermal conductor element or the temperature sensor is provided behind a function key or a dummy function key of a functional unit. The function key extends through an opening in the front cover of the functional unit, whereby the thermal conductor element also extends through this opening. If a dummy functional key projects as an integral part from the front cover into the interior, the situation described above is obtained.